We are investigating the mechanisms by which avian RNA tumor viruses replicate and induce neoplastic transformation of host cells. We hope to elucidate the role of the host cell in modulating viral gene expression, the phylogenetic origins of viral genes, and the pathways by which different viruses transform cells of both identical and different embryological lineage. The work subsumes the following major projects: (1) determination of nucleotide sequences in viral genomes and identification of functionally important regions in these sequences; (2) description of the mechanisms by which viral DNA is synthesized by reverse transcriptase and integrated into the host chromosomes; (3) characterization of endogenous viral genes that are intrinsic to the uninfected cells of vertebrate species; (4) elucidation of the means by which viral mRNAs are generated; (5) identification of cellular factors involved in viral replication and viral gene expression; and (6) identification and characterization of viral proteins responsible for neoplastic transformation of infected cells. Our techniques include: (1) analysis of nucleotide sequence in DNA and RNA; (2) enzymatic synthesis and modification of nucleic acids; (3) molecular hybridization; (4) immunoprecipitation; (5) purification of nucleic acids and proteins; (6) electron microscopy; (7) fragmentation of DNA with bacterial restriction nucleases; (8) transfer of nucleic acids from agarose gels to either membrane filters or chemically derivatized paper for subsequent molecular hybridization; and (9) the use of conditional and non-conditional viral mutants.